1. Field of the Invention
The present invention relates generally to electronics apparatus such as exclusive-use micro-controllers and, more particularly to an electronics apparatus in which a central processing unit (CPU) provided as an address controller or the like and a read-only memory (ROM) in which programs and data are stored in a fixed condition are integrated as one chip.
2. Description of the Related Art
Conventional electronics apparatus such as a video cassette recorder (VCR) having a built-in camera, for example, have mounted thereon a custom LSI (large scale integration) integrated electronics apparatus on one chip as control means, i.e., a so-called micro-controller for controlling the entirety or part of the electronics apparatus.
The micro-controller is an exclusive-use microcomputer which is composed of a central processing unit (CPU), a memory such as a read-only memory (ROM) and a random access memory (RAM) and a peripheral circuit such as an input/output (I/O) port or the like.
The CPU acts as an address controller to control the access to the memories or the like or acts as a processor to execute a program. Information such as programs, data and so on for controlling the mounted electronics device are stored in the ROM in the form of firmware. The RAM provides the CPU with a working area or the like to execute a program and the peripheral circuit is used to communicate with the external circuits. Accordingly, mass-production is indispensable for providing inexpensive custom LSI electronics apparatus such as micro-controllers or the like.
The firmware capacity stored in the ROM of the micro-controller is increased yearly as the performance of the electronics apparatus is enhanced and refined. Considering a VCR having a built-in camera, for example, the above-mentioned capacity is expected to exceed the present capacity of several 10s of kilobytes and to exceed 100k bytes after a few years.
The largest efforts are made to improve on the quality of the firmware by structured programming and various inspections so as to prevent bugs from taking place in the firmware after the micro-controller is mass-produced. Even when a bug is discovered after the micro-controller is mass-produced, a lot of money, plenty of time and people are needed to cope with the bugs by some suitable means such as correcting the firmware by the addition of an external circuit or the like and by mass-producing and exchanging a micro-controller in which a bug patch is carried out. However, in the case of electronics apparatus such as the built-in camera type VCR which uses assembly parts of high accuracy, a bug patch by the addition of an external circuit becomes substantially impossible.